ANALYTICAL CHEMISTRY
1452 spots separated by 1 cm. or more are sxtisf:tctory. \Vith strong gamma-ray sources-Xaz4, for example-more separation is desirable, as in general the t'ube cross section is the slit size. For gamma measurements a slit constructed of thicker aluminum or denser metals, such as lead, would improve the resolution; however, sources of the order of 50 to 1000 times the intensity of beta sources are required to j+ld the corresponding counting rate.
The growth and decay characteristics of radioactivity are also valuable in identifying an element. The Pb210 in R a D E F has too n-eak a beta to be detected with ordinary counting arrangements, but it can be located h y the growth of Bi210or P0210. Use was made of decay in the differentiation of nickel (Yi65) from iron ( F e 9 and zinc ( Z 1 i 6 ~ ) zinc , from iron and cobalt, and manganese from zinc. If sufficient time is allowed between siiccessive scannings for one coniponcnt to decay away, the subsequent *canning will show one less peak. In the case of the iron, nickel, and W zinc the nickel decays away first I n i t i a l 5 (2.6-hour half-life). Nest the ziiic 24 Hour Decay decays away (13.8-hour half-life) 5000 Zn 3 Day Decay K W :ind leaves the iron (46-day halfn !ife), Figure 11. 4 difference of ln half-life of a factor of at least 2 is 3 tiesirable. Furthermore. a coni1000 ponent cannot he considered (le0 c.:i!-ed away until about d half-lives 10 15 20 have elapsed. 5 Chi. One application of paper c~111,oiii:itography with radioactive niatei,i;ils Figure 11. Identification of Iroii, \-icLcI. arid Z i n c which differs from the usual use of In butanol-pyridine with diphrn? laniine solvent tracers is the detection of mdiochemical impurities (6). The definition of the spots by scanning is, in general, not so Irradiated materials, rithcr supposedly pure materials or i n precise as that obtained by autoradiography, but it has thc adactivation analysis, may rontain radioactive impurities. Paper vantage of speed and does not require additional operations to obchromatography is a convenient aiiaiytical technique, ns it retain information about the distribution of the material in the quires small amounts of the mat,erials and little effort. T!ic spots. The accuracy of the measurements depends principally authors have separated cobalt activity (Co50)from gross ainoui1t.q upon hxing the position of the source, upon the time coiiatant of of iron (FeB, Febg), cobalt (Co68) from nickel targets, and imput,ithe counting-rate meter, and upon the self-absorption in the paties from zirconium targets. If desirable, the quantities of the per. For most of the activities used (beta mauimum riiergy impurities can be measured; however, a t this time the authors greater than 0.3 m.e.v.) the self-absorption of the, w u i ce is have only indicated qualitatively that the separation can be carnegligible. With counting rates greater than 2000 t-ouiits per ried out. Quantitative determinations would involve calibraminute the error in the counting rate is about =t4% stantlard tion of the counting arrangcnient. deviation. Successive scannings of a chromatogram ith the ACliSOWLEDGXIE4T automatic scanning device differed by as much as 20% if care were not taken to keep the distance constant from the Geiger tube The authors wish to express thrir appreciation to the staff of the to the chromatogram. With proper guides this could be reduced Speraial Training Division. Oak Ridge Institute of Suclesr Studto the order of 5%. ies, for their interest anti (booperation in this investigation. This The scanning method can be used alone or in combination 15 ith work n-as supported by I-SAIX contract No. AT-40-1-Gcn-33. conventional tests. I n the case of titanium-scandium, thc titaThc first-nanied author ivoiked uiitier Fellowship contract So. 26. nium was located by s-diphenylcarbazide and the scandium t,y counting. I n the case of iron-cobalt, visible bands could be 01)LITERATURE CITED served and compared with the activity curves. The chemical (lj Benson, Bassham, Calvin, Goodale, Haas, and Stepka. . I . - 1 ~ . tests for sodium and potassium are not particularly good and Chem. SOC.,72, 1710 (1950). counting was more eatisfactory. When one works at extreme ( 2 ) Bournsnell, Nature, 165,399 (1950). dilutions, as in the case of R a D E F solutionq, there are too few (3) Calvin and Benson, S c i e w e , 109, 140 (1949). Bi211 or Poz10 atoms for most chemical tests. Radioactive (4) Fink and Fink, Ibid., 107, 253 (1948). ( 5 ) Frierson and Ammons, J . Ckem. Education, 27, 37 (1950,. nieasurements are necessary and sufficient for these locations. (6) Hume, ANAL.CHEM.,21, 322 (1949). Besides the simple location of position and concentration, the (7) LaCourt e l a l . , Nature, 163,999 (1949). properties of the radiation may be used to differentiate one ele( 8 ) Lindberg and Hummel, Arkiz: Kemi,1. 17 (1948). (9) Muller and Wise, ANAL.CHEM.,23, 207 (1951). ment from another. Such distinctions make use of the difference (10) Tishkoff, Bennett, Bennett, and Miller, S c i e n c r , 110, 452 in type of radiation, the energy of radiation, and the decay char(1949). acteristics of the activity. (11) Tomarelli and Florey, f b i d . . 107, 630 (1948). The energy of radiation of two activities may differ sufit3iently RECEIVED January 8 . 1951. Presented before the Southwide Chenliral Conto make possible a distinction. and C058differ in heta-enference October 1 7 , 1950, A t l a n t a . Ga. ergy. Different counting techniques were used to dlstinguish these activities. -4more subtle separation was carried out \qitli Na24 and K42. The maximum beta-energy of K42is greater than that of Na24. By the proper selection of an aluminum absorber and comparing the counting rates, potassium can be diffri entiated from sodium, ' 4 similar type of comparison of the gamma countI11 the article 011 .'Saponification of Difficul ly Sapolihablc ing rate of Na*4 and K42 was made using lead absorbers. I n this Esters" [ANAL.CHEY.,23, 1126 (1951)l the second result in the caie the X a z 4shows a higher gamma counting rate than the K". first column of Table I11 on page 1128 should be 255.6 instead The technique has been applied to a system where the t\\a peaks W. E. YHAEFEK of 225.6. overlap.
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Saponification of Difficultly Saponifiable Esters-Correction
